1. 3.2: Chromosomes

2. Prokaryotes One chromosome (single copy of each gene).
DNA is not associated with proteins (naked).
Plasmids are present in prokaryotes in MOST cases.
The only time a prokaryote has a copy of each gene is immediately before cell division.

3. Plasmids Typically only found in prokaryotes
Contain some useful DNA e.g. genes for antibiotic resistance
Can easily transferred between cells – even between species.
Scientific research takes advantage of these traits.
John Cairns produced images of DNA molecules that really helped to develop our understanding of DNA (1960’s). HWK, read about this on page 150/51.

4. Eukaryotes
DNA is linear
A long single strand

5. Each bead is a nucleosome
Beads on a string
Each bead is a nucleosome
A nucleosome is DNA wrapped around 8 histones.
DNA has negative charge, histone is positive.
DNA becomes condensed/supercoiled. Forming chromosomes.
Histone is a protein – DNA organisation.
Wrapped DNA inaccessible to transcription enzymes, this regulates transcription. Only certain areas of DNA molecule can be used to synthesize proteins at any one time.

6. Nucleosome
Nucleosome is a fairly large complex of 8 proteins and 146 nucleotides-long DNA.

7. Chromosome terminology
Telomere
2. Centromere
3. Short chromatid
4. Long chromatid

8. Task
What is the Human genome project? Dates? Aims? Findings?
What were the techniques used in the project?
Where did the material come from? Ethical considerations?
Who ‘controls’ this information? How should/could it be used?
Junk/satellite DNA, what? Why?
Future applications of this research?

10. The Human Genome. The complete sequence of Human DNA.
Genome of eukaryotes has lots of highly repetitive sequences. (5-45% of total genome). Between 5 – 300 base pairs per repetitive sequence.
Satellite DNA – repetitive DNA clustered in discrete areas. Also known as ‘junk DNA’
It is thought dispersed DNA has no specific coding function, but can move from one location to another (transposable elements). Importance not yet understood.
Who is Barbara McClintock?
American researcher – awarded the Nobel Prize in 1983 for her work.
She demonstrated that genes are responsible for physical characteristics (suppression/expression of genes) researched with maize plants.
Also, one of the few women to be awarded the Nobel Prize for unshared work.

11. Homologous chromosomes
Defined as: Two chromosomes carrying the same sequence of genes.
Not identical because although the genes are the same, the alleles are different.
Human chromosomes are too narrow to be viewed except when undergoing division. Humans have 23 types of chromosomes. Each chromosome carries a specific sequence of genes. Each gene has a specific location on its chromosome. This organisation is important so material can be easily exchanged during meiosis.

12. Guess the genome…
E. Coli
5 million base pairs
Plant? Animal? Pro? Eu?

13. Paris Japonica
150,000 million base pairs

14. T2 phage (virus)
0.18 million base pairs
T2 phage attacks E. coli

15. Drosophila melangaster
140 million base pairs
Fruit fly

16. Homo sapiens
3000 million base pairs

17. A - ancestral Eutherian B - Chicken C - Short-tailed opossum
D - Aardvark
E - Mink
F - Red fox
G - Ancestral Sciuridae
H - Mouse
I - Human
Ancestral Eutherian = early mammal
Opossum = mousy, longer nose
Ancestral Sciuridae = early squirrel type mammals
Organisms must have the same number of chromosomes in order to interbreed. The number of chromosomes in a species does not change easily – remain the same for millions of years.

18. Locus of a gene
The position of a gene on a chromosome

19. Haploid V’s Diploid Haploid nuclei Diploid nuclei
23 chromosomes (humans)
Gametes (sex cells)
Single copy of each gene
23 chromosome pairs
Haploids fuse to form zygote
Two copies of each gene
Di for two!
Reproduction by fusing haploid cells leads to much greater variation, reduced chance of inheriting recessive mutations & increased hybrid vigour (stronger offspring – sometimes!).

20. Who has the most chromosomes?
Data based qu. Pg. 156 78 24

21. Who has the most chromosomes?
These are diploid numbers 46 48

22. Sex chromosomes
Female: XX
Male: XY X XX Y XY
50% F
50% M
Every time!

23. Karyotyping & karyograms
Normal boy

24. Normal female

25. Downs’ affected boy

26. Downs syndrome
Definition?
Causes?
Diagnosis?
Risk factors?
Prevalence?
Treatment?

27. Observing mitosis in garlic root tip
biology/investigating-mitosis-allium-root-tip-squash